Sometimes I've seen "Dhewa" and/or "Dhakini" in Tibetan texts instead of the usual "Dewa"/"Dakini". Is this just a transliteration error from Sanskrit, or is there some other reason for it? Is there any Sanskrit precedent for using the aspirated forms?

Btw, in my original question I'm referring to transliteration from Sanskrit to Tibetan - not to the roman alphabet. Since the Tibetan script was made for transliterating Sanskrit, I would think there would be less "creative transliteration" - pretty straightforward.